On Tue, 17 May 2016 11:27:27 -0500, Tim Wescott wrote:> On Tue, 17 May 2016 08:15:42 -0500, John S wrote: > >> On 5/17/2016 1:41 AM, Tim Wescott wrote: >>> I've just spent over two weeks getting ready to do my next video. It >>> was a combination of one of those vast underestimations one >>> occasionally makes, combined with falling into a bit of an obsession. >>> >>> I am, at this point, not only wondering if it was worth it, but >>> questioning my sanity in carrying on even when the going went beyond >>> tough to just plain crazy. >>> >>> At any rate, a good video needs a visual aid, and I decided that my >>> video needed to demonstrate stability with a pendulum. Moreover, it >>> needed a pendulum that could be worked electronically. So, I've >>> >>> * Disassembled a hard drive for it's head positioner. This took a day >>> or two. >>> >>> * Decided that wasn't good enough and wound my own custom coil (220 >>> feet of #40 wire, woo hoo!). This took a false start (18 feet of #34 >>> wire) and several days. >>> >>> * Mounted the coil into a custom pendulum, running on Real Ball >>> Bearings. Several more days, and if you touch it wrong the Q goes >>> down from about 80 to about 10, then you have to fiddle with it for >>> several minutes so the moving parts don't rub. >>> >>> * Built an oscillator that uses the pendulum as its resonator (this is >>> where stability comes in -- is an oscillator stable? How is it >>> stable? >>> What if it's showing chaotic behavior?). This was astonishingly >>> frustrating, and didn't finally work until I carefully modeled the >>> pendulum as a resonator AND took the coil inductance into account in >>> the circuit. This part too about a week. >>> >>> And for all that, I now have the time base for an exceptionally >>> inaccurate electro-mechanical clock! Check out the picture. That's >>> one cycle of the pendulum, running off of a "tick-toc" circuit that >>> (A) >>> minimizes the load on the pendulum (to give a high loaded Q, essential >>> for wringing as much accuracy as possible out of a pendulum, never >>> mind that it's made of wood, masking tape, and car parts that I picked >>> up off the floor), and (B) has to be started by hand (I wanted to >>> demonstrate a hard limit cycle). >>> >>> http://wescottdesign.com/movies/stability_teaser.gif >>> >>> More on all of this when I post the video. >>> >>> >> For your next demo, use an electromagnet to lift a metal ball and hold >> it suspended. Sense the height with a light sensor. Use PID to achieve >> stability. >> >> I saw an article that did this 30 or so years ago. They used a hollow >> steel ball with a map of the earth painted on. Can't remember the >> diameter of the ball, but maybe 1". > > https://www.electronics-related.com/showarticle/526/levitating-globe- > teardown-part-1 > > https://www.electronics-related.com/showarticle/527/levitating-globe- > teardown-part-2Try that again: <https://www.electronics-related.com/showarticle/526/levitating-globe- teardown-part-1> <https://www.electronics-related.com/showarticle/527/levitating-globe- teardown-part-2> -- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
Stability and Insanity
Started by ●May 17, 2016
Reply by ●May 17, 20162016-05-17
Reply by ●May 17, 20162016-05-17
On 5/17/2016 10:54 AM, Tim Wescott wrote:> On Tue, 17 May 2016 08:15:42 -0500, John S wrote: > >> On 5/17/2016 1:41 AM, Tim Wescott wrote: >>> I've just spent over two weeks getting ready to do my next video. It >>> was a combination of one of those vast underestimations one >>> occasionally makes, combined with falling into a bit of an obsession. >>> >>> I am, at this point, not only wondering if it was worth it, but >>> questioning my sanity in carrying on even when the going went beyond >>> tough to just plain crazy. >>> >>> At any rate, a good video needs a visual aid, and I decided that my >>> video needed to demonstrate stability with a pendulum. Moreover, it >>> needed a pendulum that could be worked electronically. So, I've >>> >>> * Disassembled a hard drive for it's head positioner. This took a day >>> or two. >>> >>> * Decided that wasn't good enough and wound my own custom coil (220 >>> feet of #40 wire, woo hoo!). This took a false start (18 feet of #34 >>> wire) and several days. >>> >>> * Mounted the coil into a custom pendulum, running on Real Ball >>> Bearings. Several more days, and if you touch it wrong the Q goes down >>> from about 80 to about 10, then you have to fiddle with it for several >>> minutes so the moving parts don't rub. >>> >>> * Built an oscillator that uses the pendulum as its resonator (this is >>> where stability comes in -- is an oscillator stable? How is it stable? >>> What if it's showing chaotic behavior?). This was astonishingly >>> frustrating, and didn't finally work until I carefully modeled the >>> pendulum as a resonator AND took the coil inductance into account in >>> the circuit. This part too about a week. >>> >>> And for all that, I now have the time base for an exceptionally >>> inaccurate electro-mechanical clock! Check out the picture. That's >>> one cycle of the pendulum, running off of a "tick-toc" circuit that (A) >>> minimizes the load on the pendulum (to give a high loaded Q, essential >>> for wringing as much accuracy as possible out of a pendulum, never mind >>> that it's made of wood, masking tape, and car parts that I picked up >>> off the floor), and (B) has to be started by hand (I wanted to >>> demonstrate a hard limit cycle). >>> >>> http://wescottdesign.com/movies/stability_teaser.gif >>> >>> More on all of this when I post the video. >>> >>> >> For your next demo, use an electromagnet to lift a metal ball and hold >> it suspended. Sense the height with a light sensor. Use PID to achieve >> stability. >> >> I saw an article that did this 30 or so years ago. They used a hollow >> steel ball with a map of the earth painted on. Can't remember the >> diameter of the ball, but maybe 1". > > I've done that. You need a honkin' big electromagnet to make it work > with a plain steel load. > > The executive desk-toys with the floating globes use big (30mm dia x > 10mm) rare-earth magnets, and float the ball a little bit below the > neutral point. I believe that they use hall effect sensors to detect the > magnet proximity. >Oops! Sorry! I didn't know you were already doing it. Cheers.
Reply by ●May 17, 20162016-05-17
On Tue, 17 May 2016 11:52:12 -0500, John S wrote:> On 5/17/2016 10:54 AM, Tim Wescott wrote: >> On Tue, 17 May 2016 08:15:42 -0500, John S wrote: >> >>> On 5/17/2016 1:41 AM, Tim Wescott wrote: >>>> I've just spent over two weeks getting ready to do my next video. It >>>> was a combination of one of those vast underestimations one >>>> occasionally makes, combined with falling into a bit of an obsession. >>>> >>>> I am, at this point, not only wondering if it was worth it, but >>>> questioning my sanity in carrying on even when the going went beyond >>>> tough to just plain crazy. >>>> >>>> At any rate, a good video needs a visual aid, and I decided that my >>>> video needed to demonstrate stability with a pendulum. Moreover, it >>>> needed a pendulum that could be worked electronically. So, I've >>>> >>>> * Disassembled a hard drive for it's head positioner. This took a >>>> day or two. >>>> >>>> * Decided that wasn't good enough and wound my own custom coil (220 >>>> feet of #40 wire, woo hoo!). This took a false start (18 feet of #34 >>>> wire) and several days. >>>> >>>> * Mounted the coil into a custom pendulum, running on Real Ball >>>> Bearings. Several more days, and if you touch it wrong the Q goes >>>> down from about 80 to about 10, then you have to fiddle with it for >>>> several minutes so the moving parts don't rub. >>>> >>>> * Built an oscillator that uses the pendulum as its resonator (this >>>> is where stability comes in -- is an oscillator stable? How is it >>>> stable? >>>> What if it's showing chaotic behavior?). This was astonishingly >>>> frustrating, and didn't finally work until I carefully modeled the >>>> pendulum as a resonator AND took the coil inductance into account in >>>> the circuit. This part too about a week. >>>> >>>> And for all that, I now have the time base for an exceptionally >>>> inaccurate electro-mechanical clock! Check out the picture. That's >>>> one cycle of the pendulum, running off of a "tick-toc" circuit that >>>> (A) >>>> minimizes the load on the pendulum (to give a high loaded Q, >>>> essential for wringing as much accuracy as possible out of a >>>> pendulum, never mind that it's made of wood, masking tape, and car >>>> parts that I picked up off the floor), and (B) has to be started by >>>> hand (I wanted to demonstrate a hard limit cycle). >>>> >>>> http://wescottdesign.com/movies/stability_teaser.gif >>>> >>>> More on all of this when I post the video. >>>> >>>> >>> For your next demo, use an electromagnet to lift a metal ball and hold >>> it suspended. Sense the height with a light sensor. Use PID to achieve >>> stability. >>> >>> I saw an article that did this 30 or so years ago. They used a hollow >>> steel ball with a map of the earth painted on. Can't remember the >>> diameter of the ball, but maybe 1". >> >> I've done that. You need a honkin' big electromagnet to make it work >> with a plain steel load. >> >> The executive desk-toys with the floating globes use big (30mm dia x >> 10mm) rare-earth magnets, and float the ball a little bit below the >> neutral point. I believe that they use hall effect sensors to detect >> the magnet proximity. >> >> > Oops! Sorry! I didn't know you were already doing it.Well, the project is on long-term hold, but I did get as far as getting one of those desk toys and starting to take it apart. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
Reply by ●May 17, 20162016-05-17
On 5/17/2016 11:57 AM, Tim Wescott wrote:> On Tue, 17 May 2016 11:52:12 -0500, John S wrote: > >> On 5/17/2016 10:54 AM, Tim Wescott wrote: >>> On Tue, 17 May 2016 08:15:42 -0500, John S wrote: >>> >>>> On 5/17/2016 1:41 AM, Tim Wescott wrote: >>>>> I've just spent over two weeks getting ready to do my next video. It >>>>> was a combination of one of those vast underestimations one >>>>> occasionally makes, combined with falling into a bit of an obsession. >>>>> >>>>> I am, at this point, not only wondering if it was worth it, but >>>>> questioning my sanity in carrying on even when the going went beyond >>>>> tough to just plain crazy. >>>>> >>>>> At any rate, a good video needs a visual aid, and I decided that my >>>>> video needed to demonstrate stability with a pendulum. Moreover, it >>>>> needed a pendulum that could be worked electronically. So, I've >>>>> >>>>> * Disassembled a hard drive for it's head positioner. This took a >>>>> day or two. >>>>> >>>>> * Decided that wasn't good enough and wound my own custom coil (220 >>>>> feet of #40 wire, woo hoo!). This took a false start (18 feet of #34 >>>>> wire) and several days. >>>>> >>>>> * Mounted the coil into a custom pendulum, running on Real Ball >>>>> Bearings. Several more days, and if you touch it wrong the Q goes >>>>> down from about 80 to about 10, then you have to fiddle with it for >>>>> several minutes so the moving parts don't rub. >>>>> >>>>> * Built an oscillator that uses the pendulum as its resonator (this >>>>> is where stability comes in -- is an oscillator stable? How is it >>>>> stable? >>>>> What if it's showing chaotic behavior?). This was astonishingly >>>>> frustrating, and didn't finally work until I carefully modeled the >>>>> pendulum as a resonator AND took the coil inductance into account in >>>>> the circuit. This part too about a week. >>>>> >>>>> And for all that, I now have the time base for an exceptionally >>>>> inaccurate electro-mechanical clock! Check out the picture. That's >>>>> one cycle of the pendulum, running off of a "tick-toc" circuit that >>>>> (A) >>>>> minimizes the load on the pendulum (to give a high loaded Q, >>>>> essential for wringing as much accuracy as possible out of a >>>>> pendulum, never mind that it's made of wood, masking tape, and car >>>>> parts that I picked up off the floor), and (B) has to be started by >>>>> hand (I wanted to demonstrate a hard limit cycle). >>>>> >>>>> http://wescottdesign.com/movies/stability_teaser.gif >>>>> >>>>> More on all of this when I post the video. >>>>> >>>>> >>>> For your next demo, use an electromagnet to lift a metal ball and hold >>>> it suspended. Sense the height with a light sensor. Use PID to achieve >>>> stability. >>>> >>>> I saw an article that did this 30 or so years ago. They used a hollow >>>> steel ball with a map of the earth painted on. Can't remember the >>>> diameter of the ball, but maybe 1". >>> >>> I've done that. You need a honkin' big electromagnet to make it work >>> with a plain steel load. >>> >>> The executive desk-toys with the floating globes use big (30mm dia x >>> 10mm) rare-earth magnets, and float the ball a little bit below the >>> neutral point. I believe that they use hall effect sensors to detect >>> the magnet proximity. >>> >>> >> Oops! Sorry! I didn't know you were already doing it. > > Well, the project is on long-term hold, but I did get as far as getting > one of those desk toys and starting to take it apart. >Would it be inappropriate to demonstrate PID? Just curious.
Reply by ●May 17, 20162016-05-17
On Tue, 17 May 2016 12:02:12 -0500, John S wrote:> On 5/17/2016 11:57 AM, Tim Wescott wrote: >> On Tue, 17 May 2016 11:52:12 -0500, John S wrote: >> >>> On 5/17/2016 10:54 AM, Tim Wescott wrote: >>>> On Tue, 17 May 2016 08:15:42 -0500, John S wrote: >>>> >>>>> On 5/17/2016 1:41 AM, Tim Wescott wrote: >>>>>> I've just spent over two weeks getting ready to do my next video. >>>>>> It was a combination of one of those vast underestimations one >>>>>> occasionally makes, combined with falling into a bit of an >>>>>> obsession. >>>>>> >>>>>> I am, at this point, not only wondering if it was worth it, but >>>>>> questioning my sanity in carrying on even when the going went >>>>>> beyond tough to just plain crazy. >>>>>> >>>>>> At any rate, a good video needs a visual aid, and I decided that my >>>>>> video needed to demonstrate stability with a pendulum. Moreover, >>>>>> it needed a pendulum that could be worked electronically. So, I've >>>>>> >>>>>> * Disassembled a hard drive for it's head positioner. This took a >>>>>> day or two. >>>>>> >>>>>> * Decided that wasn't good enough and wound my own custom coil (220 >>>>>> feet of #40 wire, woo hoo!). This took a false start (18 feet of >>>>>> #34 wire) and several days. >>>>>> >>>>>> * Mounted the coil into a custom pendulum, running on Real Ball >>>>>> Bearings. Several more days, and if you touch it wrong the Q goes >>>>>> down from about 80 to about 10, then you have to fiddle with it for >>>>>> several minutes so the moving parts don't rub. >>>>>> >>>>>> * Built an oscillator that uses the pendulum as its resonator (this >>>>>> is where stability comes in -- is an oscillator stable? How is it >>>>>> stable? >>>>>> What if it's showing chaotic behavior?). This was astonishingly >>>>>> frustrating, and didn't finally work until I carefully modeled the >>>>>> pendulum as a resonator AND took the coil inductance into account >>>>>> in the circuit. This part too about a week. >>>>>> >>>>>> And for all that, I now have the time base for an exceptionally >>>>>> inaccurate electro-mechanical clock! Check out the picture. >>>>>> That's one cycle of the pendulum, running off of a "tick-toc" >>>>>> circuit that (A) >>>>>> minimizes the load on the pendulum (to give a high loaded Q, >>>>>> essential for wringing as much accuracy as possible out of a >>>>>> pendulum, never mind that it's made of wood, masking tape, and car >>>>>> parts that I picked up off the floor), and (B) has to be started by >>>>>> hand (I wanted to demonstrate a hard limit cycle). >>>>>> >>>>>> http://wescottdesign.com/movies/stability_teaser.gif >>>>>> >>>>>> More on all of this when I post the video. >>>>>> >>>>>> >>>>> For your next demo, use an electromagnet to lift a metal ball and >>>>> hold it suspended. Sense the height with a light sensor. Use PID to >>>>> achieve stability. >>>>> >>>>> I saw an article that did this 30 or so years ago. They used a >>>>> hollow steel ball with a map of the earth painted on. Can't remember >>>>> the diameter of the ball, but maybe 1". >>>> >>>> I've done that. You need a honkin' big electromagnet to make it work >>>> with a plain steel load. >>>> >>>> The executive desk-toys with the floating globes use big (30mm dia x >>>> 10mm) rare-earth magnets, and float the ball a little bit below the >>>> neutral point. I believe that they use hall effect sensors to detect >>>> the magnet proximity. >>>> >>>> >>> Oops! Sorry! I didn't know you were already doing it. >> >> Well, the project is on long-term hold, but I did get as far as getting >> one of those desk toys and starting to take it apart. >> >> > Would it be inappropriate to demonstrate PID? Just curious.I suspect that it would be a good way to demonstrate a number of principles in control systems, PID controllers included. A lot of people seem to separate "PID" from other controllers -- somewhere in this thread someone made a comment about "oh, that wouldn't work with a PID controller". Yet most advanced controllers really boil down to a PID controller with: * A different way of arriving at the gains; * various linear and nonlinear decorations; * and a fancy name. But -- that's a rant for another day. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
Reply by ●May 17, 20162016-05-17
On Tue, 17 May 2016 09:34:06 -0400, Phil Hobbs wrote:> Found it. It was _fifty_ years ago: > > http://www.coilgun.info/lev_popelex1966/home.htm > > Cheers > > Phil "Old magazines rule" HobbsUsenet: bringing out the best in Humanity. <3 How else would I (a) find such a web site and (b) get the idea that I should have a levitating atlas thingy on my desk?
Reply by ●May 17, 20162016-05-17
On 05/17/2016 01:30 PM, Tim Wescott wrote:> On Tue, 17 May 2016 12:02:12 -0500, John S wrote: > >> On 5/17/2016 11:57 AM, Tim Wescott wrote: >>> On Tue, 17 May 2016 11:52:12 -0500, John S wrote: >>> >>>> On 5/17/2016 10:54 AM, Tim Wescott wrote: >>>>> On Tue, 17 May 2016 08:15:42 -0500, John S wrote: >>>>> >>>>>> On 5/17/2016 1:41 AM, Tim Wescott wrote: >>>>>>> I've just spent over two weeks getting ready to do my next video. >>>>>>> It was a combination of one of those vast underestimations one >>>>>>> occasionally makes, combined with falling into a bit of an >>>>>>> obsession. >>>>>>> >>>>>>> I am, at this point, not only wondering if it was worth it, but >>>>>>> questioning my sanity in carrying on even when the going went >>>>>>> beyond tough to just plain crazy. >>>>>>> >>>>>>> At any rate, a good video needs a visual aid, and I decided that my >>>>>>> video needed to demonstrate stability with a pendulum. Moreover, >>>>>>> it needed a pendulum that could be worked electronically. So, I've >>>>>>> >>>>>>> * Disassembled a hard drive for it's head positioner. This took a >>>>>>> day or two. >>>>>>> >>>>>>> * Decided that wasn't good enough and wound my own custom coil (220 >>>>>>> feet of #40 wire, woo hoo!). This took a false start (18 feet of >>>>>>> #34 wire) and several days. >>>>>>> >>>>>>> * Mounted the coil into a custom pendulum, running on Real Ball >>>>>>> Bearings. Several more days, and if you touch it wrong the Q goes >>>>>>> down from about 80 to about 10, then you have to fiddle with it for >>>>>>> several minutes so the moving parts don't rub. >>>>>>> >>>>>>> * Built an oscillator that uses the pendulum as its resonator (this >>>>>>> is where stability comes in -- is an oscillator stable? How is it >>>>>>> stable? >>>>>>> What if it's showing chaotic behavior?). This was astonishingly >>>>>>> frustrating, and didn't finally work until I carefully modeled the >>>>>>> pendulum as a resonator AND took the coil inductance into account >>>>>>> in the circuit. This part too about a week. >>>>>>> >>>>>>> And for all that, I now have the time base for an exceptionally >>>>>>> inaccurate electro-mechanical clock! Check out the picture. >>>>>>> That's one cycle of the pendulum, running off of a "tick-toc" >>>>>>> circuit that (A) >>>>>>> minimizes the load on the pendulum (to give a high loaded Q, >>>>>>> essential for wringing as much accuracy as possible out of a >>>>>>> pendulum, never mind that it's made of wood, masking tape, and car >>>>>>> parts that I picked up off the floor), and (B) has to be started by >>>>>>> hand (I wanted to demonstrate a hard limit cycle). >>>>>>> >>>>>>> http://wescottdesign.com/movies/stability_teaser.gif >>>>>>> >>>>>>> More on all of this when I post the video. >>>>>>> >>>>>>> >>>>>> For your next demo, use an electromagnet to lift a metal ball and >>>>>> hold it suspended. Sense the height with a light sensor. Use PID to >>>>>> achieve stability. >>>>>> >>>>>> I saw an article that did this 30 or so years ago. They used a >>>>>> hollow steel ball with a map of the earth painted on. Can't remember >>>>>> the diameter of the ball, but maybe 1". >>>>> >>>>> I've done that. You need a honkin' big electromagnet to make it work >>>>> with a plain steel load. >>>>> >>>>> The executive desk-toys with the floating globes use big (30mm dia x >>>>> 10mm) rare-earth magnets, and float the ball a little bit below the >>>>> neutral point. I believe that they use hall effect sensors to detect >>>>> the magnet proximity. >>>>> >>>>> >>>> Oops! Sorry! I didn't know you were already doing it. >>> >>> Well, the project is on long-term hold, but I did get as far as getting >>> one of those desk toys and starting to take it apart. >>> >>> >> Would it be inappropriate to demonstrate PID? Just curious. > > I suspect that it would be a good way to demonstrate a number of > principles in control systems, PID controllers included. > > A lot of people seem to separate "PID" from other controllers -- > somewhere in this thread someone made a comment about "oh, that wouldn't > work with a PID controller". Yet most advanced controllers really boil > down to a PID controller with: > > * A different way of arriving at the gains; > * various linear and nonlinear decorations; > * and a fancy name. > > But -- that's a rant for another day. >Well, there are various lead-lag type tricks that require basically lowpass filtering the D term. PLLs and diffusion-dominated temperature controls don't like terms with huge noise gain. When I was a post-doc, in about 1988, I did a motion controller for a piezo bimorph used in a scanning force microscope. It had a notch filter for the lowest resonance, two integrators (with lead-lag to make the loop stable) and two more poles to get rid of wideband crap that would excite the higher resonances. Worked great--when tweaked for best settling time, the loop BW was about 30% of the resonant frequency, vs. 3% for the previous version. (The resonance had a Q of about 30, so with just one integrator and no notch, the BW had to be backed off a really long way to prevent oscillation.) Would you include that in "decorated PID"? I generally do it that way, i.e. use frequency compensation ideas, concentrate on phase margin, and then watch out for the transient response, because when you do something fancy like the above, the settling behaviour is liable to be a bit strange. Of course when one of my loops misbehaves a bit during testing, no machinery is ruined and nobody gets hurt. Windup and nonlinear slewing are sometimes issues too, of course. Overall it seems like the distinction between control guys and other EEs is a bit like the difference between civil and mechanical--a lot of the same concepts but completely different emphasis. Is that fair? Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●May 17, 20162016-05-17
On 05/17/2016 01:40 PM, Aleksandar Kuktin wrote:> On Tue, 17 May 2016 09:34:06 -0400, Phil Hobbs wrote: > >> Found it. It was _fifty_ years ago: >> >> http://www.coilgun.info/lev_popelex1966/home.htm >> >> Cheers >> >> Phil "Old magazines rule" Hobbs > > Usenet: bringing out the best in Humanity. <3 > > How else would I (a) find such a web site and (b) get the idea that I > should have a levitating atlas thingy on my desk? >;) There are better things in humanity than that. My wife's cooking, for one. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●May 17, 20162016-05-17
On 05/17/2016 01:02 PM, John S wrote:> On 5/17/2016 11:57 AM, Tim Wescott wrote: >> On Tue, 17 May 2016 11:52:12 -0500, John S wrote: >> >>> On 5/17/2016 10:54 AM, Tim Wescott wrote: >>>> On Tue, 17 May 2016 08:15:42 -0500, John S wrote: >>>> >>>>> On 5/17/2016 1:41 AM, Tim Wescott wrote: >>>>>> I've just spent over two weeks getting ready to do my next video. It >>>>>> was a combination of one of those vast underestimations one >>>>>> occasionally makes, combined with falling into a bit of an obsession. >>>>>> >>>>>> I am, at this point, not only wondering if it was worth it, but >>>>>> questioning my sanity in carrying on even when the going went beyond >>>>>> tough to just plain crazy. >>>>>> >>>>>> At any rate, a good video needs a visual aid, and I decided that my >>>>>> video needed to demonstrate stability with a pendulum. Moreover, it >>>>>> needed a pendulum that could be worked electronically. So, I've >>>>>> >>>>>> * Disassembled a hard drive for it's head positioner. This took a >>>>>> day or two. >>>>>> >>>>>> * Decided that wasn't good enough and wound my own custom coil (220 >>>>>> feet of #40 wire, woo hoo!). This took a false start (18 feet of #34 >>>>>> wire) and several days. >>>>>> >>>>>> * Mounted the coil into a custom pendulum, running on Real Ball >>>>>> Bearings. Several more days, and if you touch it wrong the Q goes >>>>>> down from about 80 to about 10, then you have to fiddle with it for >>>>>> several minutes so the moving parts don't rub. >>>>>> >>>>>> * Built an oscillator that uses the pendulum as its resonator (this >>>>>> is where stability comes in -- is an oscillator stable? How is it >>>>>> stable? >>>>>> What if it's showing chaotic behavior?). This was astonishingly >>>>>> frustrating, and didn't finally work until I carefully modeled the >>>>>> pendulum as a resonator AND took the coil inductance into account in >>>>>> the circuit. This part too about a week. >>>>>> >>>>>> And for all that, I now have the time base for an exceptionally >>>>>> inaccurate electro-mechanical clock! Check out the picture. That's >>>>>> one cycle of the pendulum, running off of a "tick-toc" circuit that >>>>>> (A) >>>>>> minimizes the load on the pendulum (to give a high loaded Q, >>>>>> essential for wringing as much accuracy as possible out of a >>>>>> pendulum, never mind that it's made of wood, masking tape, and car >>>>>> parts that I picked up off the floor), and (B) has to be started by >>>>>> hand (I wanted to demonstrate a hard limit cycle). >>>>>> >>>>>> http://wescottdesign.com/movies/stability_teaser.gif >>>>>> >>>>>> More on all of this when I post the video. >>>>>> >>>>>> >>>>> For your next demo, use an electromagnet to lift a metal ball and hold >>>>> it suspended. Sense the height with a light sensor. Use PID to achieve >>>>> stability. >>>>> >>>>> I saw an article that did this 30 or so years ago. They used a hollow >>>>> steel ball with a map of the earth painted on. Can't remember the >>>>> diameter of the ball, but maybe 1". >>>> >>>> I've done that. You need a honkin' big electromagnet to make it work >>>> with a plain steel load. >>>> >>>> The executive desk-toys with the floating globes use big (30mm dia x >>>> 10mm) rare-earth magnets, and float the ball a little bit below the >>>> neutral point. I believe that they use hall effect sensors to detect >>>> the magnet proximity. >>>> >>>> >>> Oops! Sorry! I didn't know you were already doing it. >> >> Well, the project is on long-term hold, but I did get as far as getting >> one of those desk toys and starting to take it apart. >> > > Would it be inappropriate to demonstrate PID? Just curious.A levitated ball is a nearly undamped, nonlinear second order system, which seems like a good test case. Tim's pendulum with a Q of 80 is good too, and more linear for small deflections. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●May 17, 20162016-05-17
On Tue, 17 May 2016 01:41:51 -0500, Tim Wescott <seemywebsite@myfooter.really> wrote:>I've just spent over two weeks getting ready to do my next video. It was >a combination of one of those vast underestimations one occasionally >makes, combined with falling into a bit of an obsession. > >I am, at this point, not only wondering if it was worth it, but >questioning my sanity in carrying on even when the going went beyond >tough to just plain crazy. > >At any rate, a good video needs a visual aid, and I decided that my video >needed to demonstrate stability with a pendulum. Moreover, it needed a >pendulum that could be worked electronically. So, I've > >* Disassembled a hard drive for it's head positioner. This took a day or >two. > >* Decided that wasn't good enough and wound my own custom coil (220 feet >of #40 wire, woo hoo!). This took a false start (18 feet of #34 wire) >and several days. > >* Mounted the coil into a custom pendulum, running on Real Ball >Bearings. Several more days, and if you touch it wrong the Q goes down >from about 80 to about 10, then you have to fiddle with it for several >minutes so the moving parts don't rub. > >* Built an oscillator that uses the pendulum as its resonator (this is >where stability comes in -- is an oscillator stable? How is it stable? >What if it's showing chaotic behavior?). This was astonishingly >frustrating, and didn't finally work until I carefully modeled the >pendulum as a resonator AND took the coil inductance into account in the >circuit. This part too about a week. > >And for all that, I now have the time base for an exceptionally >inaccurate electro-mechanical clock! Check out the picture. That's one >cycle of the pendulum, running off of a "tick-toc" circuit that (A) >minimizes the load on the pendulum (to give a high loaded Q, essential >for wringing as much accuracy as possible out of a pendulum, never mind >that it's made of wood, masking tape, and car parts that I picked up off >the floor), and (B) has to be started by hand (I wanted to demonstrate a >hard limit cycle). > >http://wescottdesign.com/movies/stability_teaser.gif > >More on all of this when I post the video.We seldom encounter chaotic behavior in electronic circuits... on purpose, I guess. Superregenerative receivers are kind of chaotic, but mostly just noisy. A laser driving some fiber with lots of reflections can be chaotic, but the only nonlinear element is the laser itself. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
